Virtual environments offer multiple advantages for training (e.g., risk reduction) but also include potential weaknesses. For example, adding short visual delays between a limb movement and its virtual motion representation can significantly impair visuomotor performance (Smith, 1972). Also, considering the principles of multisensory integration (Ernst & Bulthoff, 2004), it is relevant to compare visual-proprioceptive contributions to upper-limb control during virtual vs. real limb motion.
The currently study implemented visual and proprioceptive perturbations during upper-limb trajectories in real or virtual aiming environments. Participants performed reaches under a half-silvered mirror (mean movement time = 336 ms; amplitude = 25 cm; index of difficulty = 5.65) with direct vision of their hand (real) or of a cursor representing their fingertip (virtual). Further, vision of the hand or cursor was either available prior to movement onset (prior) or throughout the trajectory (prior and during). As well, simultaneous agonist-antagonist tendon vibration was present before half of the trials.
Participants exhibited significantly longer movement times and more errorful movements (i.e., increased constant and variable error) when reaching in the virtual than the real environment. Furthermore, the effect of between-trial tendon vibration yielded some mitigated evidence suggesting proprioception contributed less to upper-limb control in the virtual environment. Finally, the aforementioned differences were best explained by online control mechanisms because the sensory perturbations yielded longer limb deceleration durations.
Overall, the current study indicates that virtual environments can incur temporal and spatial costs to limb control, which appear to be linked to online sensorimotor processes.